Propellant

… what is certain, is that by the time of the Alderney ship, the gunpowder weapon, whether shoulder gun or deck cannon, was supreme at sea.

The Mary Rose and Alderney ship were at opposite ends of a revolution in naval architecture, ballistic science and tactics that all happened in less than a life time.

The single gun so far recovered from the Alderney ship was found loaded … also it was found with with its tampion in place and its touch-hole sealed with a wooden plug.

A lead cover or 'apron'. It was tied over the touch hole to prevent water penetration

Gunpowder is a sullen substance. It can become damp, the mix can degenerate and the rate of burn can vary. The guns of the Mary Rose used serpentine powder, a propellant that was highly hydroscopic (i.e. damp absorbent) and which, with time, will tend to revert to its original parts. It was also relatively slow burning which meant a less immediate eruption of pressure, which, in general terms meant that guns had to be longer to build up muzzle velocity. The moodiness of serpentine powder also meant that if the gun was under-rammed it would not combust well and thus lose much of its propulsive power, and if it was over-rammed, it might ‘hang fire’, that is to say smoulder before exploding. The problem of delayed fire while trying to hit a moving target from a gun platform that was itself pitching and rolling, hardly requires explanation.

To have the projectile move faster, and thus have greater range, and potentially greater accuracy, one could either ignite more power or improve its quality. Sometime in the second half of the 1570s, the Navy began to change its propellant for heavy ordnance from serpentine powder to corned powder which was more stable and less prone to damp, and which before had only been used for shoulder arms and hand-guns. The real value of the new propellant was that it was more powerful because it burned faster (i.e. the better mix and more granular texture allowed combustion to pass more quickly between the grains) and thus was able to produce a much increased volume of gas more quickly. Muzzle velocities were achieved of 1,300 to 1,400 ft per second which, of course, would have meant a marked improvement in range. Although, as Charles Ffoulkes, a former Master of the Armouries at the Tower of London, once wrote, ‘There is a discreet silence in all early accounts of artillery as to its effective range’, it seems likely that the Alderney guns would have been able to project a shot beyond 2,500 yards (but it is doubtful if that shot would have done much harm beyond 200 to 250 yards). There would also have been significant terminal ballistic changes, that is to say the effects of a projectile upon its target; but on this, again, we know little beyond the certainty that the weapon’s penetrative and destructive capability would have been improved.

The new powder also had an effect on the gun’s internal ballistics to the extent that its very shape and proportions had to change. First the barrel became more conical (i.e. a greater width of metal around the chamber), and second, it had to be better reinforced. Up until 1571 long guns were still being made with a single ‘reinforce’, but with the introduction of corned powder there had to be two. The introduction of corned powder also meant that the guns could become shorter without a significant sacrifice of range and power, for it had long been a tenet of gunnery (though not an entirely correct one) that ‘with equal charges, and guns of equal weight, but of different lengths, the velocity of the shot increases with the length of the bore’ (Douglas, 1820).

There was also a financial advantage to corned powder. Although the two powders cost about the same, corned powder, because of its greater power, permitted a smaller charge. With serpentine powder, the weight of charge was close to three-quarters the weight of the shot; with corned powder it was reduced to two-thirds. Figures taken from Eldred (1646) and Norton (1643), show that a successful discharge of a minion shot of 3.7 lbs would have required 3.5 lbs of serpentine powder, but only 3 lbs of corned powder.

One disadvantage of corned powder, however, was the effect it had on the weapon’s external behaviour. With the slow-burning gunpowder a relatively short breeching arrangement was enough to control the recoil, but with the introduction of corned powder the kick was manifestly more violent and could only be restrained with a heavier, lengthier roping arrangement. The Alderney minions had a ‘permitted’ recoil of perhaps six or seven feet, by contrast the larger culverins are believed to have had a recoil of about ten feet. One advantage of the increased recoil is that it would have facilitated the withinboard preparations for re-firing, particularly the swabbing of the barrel to get rid of any residues and embers, and ramming, which was necessary to ensure that there were no air-pockets at the rear of the bore. The relative ease with which these procedures were carried out, would certainly have improved the rate of fire. The Spanish and Portuguese, by contrast, did not use trucked carriages, instead their guns were often roped semi-permanently to the ship’s side, a method which compromised their reloading times.

From Board of Ordnance surveys and accounts it is clear that, in response to the more powerful powders and the resulting changes in gun design, there were also alterations and changes to the ‘breeching for the staying of great ordnance in discharging’. The ordnance historian Adrian Caruana (1994) concludes that by 1585 at latest (less than a decade before the Alderney wreck) the new breeching arrangements were complete. But what were the new breeching arrangements? The short answer is we do not know, but within the matrix of corrosion products that engulf the submerged Alderney guns, we are hopeful that some cordage will survive which will shed important light upon the general roping, knotting, tackling and ring-bolting of the new naval artillery systems that came in during the late Elizabethan era.

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